Automatic transmission control system

Abstract

An automatic transmission control system in which a specific one of friction coupling elements is selectively locked and unlocked to provide a specific gear initiates locking the specific friction coupling element to execute a gear shift to the specific gear at a level of input torque to the automatic transmission from the torque converter higher when a friction-related parameter demonstrates a high friction coefficient of the coupling element than when demonstrating a low friction coefficient.

What is claimed is: 
     
       1. A control system for an automatic transmission equipped with a torque converter and a plurality of friction coupling elements selectively locked and unlocked to provide desired gears, a specific one of said friction coupling elements being locked to provide a specific gear, said control system comprising: frictional condition monitoring means for monitoring a frictional condition of said specific friction coupling element using a friction-related parameter in relation to a friction coefficient of said specific friction coupling element;   shift control means for initiating locking of said specific friction coupling element to execute a gear shift to said specific gear at a level of input torque to said automatic transmission from said torque converter higher when said friction-related parameter demonstrates that said friction coefficient is high as compared to a predetermined friction related parameter than when said friction-related parameter demonstrates the said friction coefficient is low as compared to said predetermined friction related parameter.   
     
     
       2. An automatic transmission control system as defined in claim 1, wherein said specific friction coupling element comprises brake means including a brake drum and a brake band. 
     
     
       3. An automatic transmission control system as defined in claim 1, wherein said specific friction coupling element is locked to place said automatic transmission into a second gear as said specific gear. 
     
     
       4. An automatic transmission control system as defined in claim 1, wherein said frictional condition monitoring means comprises a temperature sensor for detecting a temperature of working oil applied to said specific friction coupling element. 
     
     
       5. An automatic transmission control system as defined in claim 1, and further comprising a torque transmission condition monitoring means for monitoring a torque transmission condition of said torque converter using a torque-related parameter in relation to a torque ratio of said torque converter, wherein said shift control means monitors said torque-related parameter, causes locking said specific friction coupling element when said torque-related parameter demonstrates a torque ratio higher than a specified decision ratio, and changes said decision ratio according to said friction-related parameter such that said gear shift is initiated at a torque ratio higher when said friction-related parameter demonstrates a high friction coefficient than when demonstrating a low friction coefficient. 
     
     
       6. An automatic transmission control system as defined in claim 5, and further comprising throttle condition monitoring means for monitoring an operated condition of an engine throttle using a throttle-related parameter in relation to throttle opening of said engine throttle, wherein said shift control means causes locking said specific friction coupling element at a high torque ratio when, while said friction-related parameter demonstrates a high friction coefficient, said throttle-related parameter demonstrates small throttle opening than when said friction-related parameter demonstrates a friction coefficient is low. 
     
     
       7. An automatic transmission control system as defined in claim 1, and further comprising a vehicle speed condition monitoring means for monitoring a speed of the vehicle using a speed-related parameter in relation to a vehicle speed of the vehicle and torque transmission condition monitoring means for monitoring a level of input torque transmitted to said automatic transmission from said torque converter, wherein said shift control means monitors said speed-related parameter, causes locking said specific friction coupling element when, while said speed-related parameter demonstrates that a vehicle speed meets a predetermined gear shift condition, said torque-related parameter demonstrates a ratio than a specified decision ratio, and changes said decision ratio such that said gear shift is initiated at a level of said input torque higher when said friction-related parameter demonstrates a high friction coefficient than when demonstrating a low friction coefficient. 
     
     
       8. An automatic transmission control system as defined in claim 1, and further comprising a shift characteristic memory means for storing predetermined first and second shift characteristics defined using parameters in relation to vehicle speed and throttle opening, wherein said shift control means causes locking said specific friction coupling element based on said first shift characteristic when said friction-related parameter demonstrates a low friction coefficient and based on said second shift characteristic when demonstrating a high friction coefficient. 
     
     
       9. An automatic transmission control system as defined in claim 8, wherein said first and second shift characteristics are established such that, for same throttle opening, a gear shift to said specified gear is caused at a speed lower if said gear shift attributes said second shift characteristic than if said gear shift attributes said first shift characteristic. 
     
     
       10. An automatic transmission control system as defined in claim 9, wherein said specific friction coupling element comprises brake means including a brake drum and a brake band. 
     
     
       11. An automatic transmission control system as defined in claim 10, wherein a gear shift from a first gear to a second gear as said specified gear is caused at a speed lower if said first to second gear shift attributes said second shift characteristic than if said first to second gear shift attributes said first shift characteristic. 
     
     
       12. An automatic transmission control system as defined in claim 1, and further comprising a shift characteristic memory means for storing predetermined a shift characteristic defined using parameters in relation to vehicle speed and throttle opening, respectively, and torque transmission condition monitoring means for monitoring a torque transmission condition of said torque converter using a torque-related parameter in relation to a torque ratio of said torque converter, wherein said shift control means causes locking said specific friction coupling element at a time defined by said shift characteristic when said friction-related parameter demonstrates a low friction coefficient and at a time when, while said friction-related parameter demonstrates a high friction coefficient, said torque-related parameter demonstrates a ratio higher than a specified decision ratio, said specified decision level being established in such a way that said gear shift is achieved at input torque higher when being caused due to said friction-related parameter demonstrating a high friction coefficient than when being caused due to said friction-related parameter demonstrating a low friction coefficient. 
     
     
       13. An automatic transmission control system as defined in claim 12, and further comprising a throttle condition monitoring means for monitoring an operated condition of an engine throttle using a throttle-related parameter in relation to throttle opening of said engine throttle, wherein said shift control means changes said decision ratio according to said throttle-related parameter. 
     
     
       14. A control system for an automatic transmission equipped with a torque converter and a plurality of friction coupling elements selectively locked and unlocked to provide desired gears, a specific one of said friction coupling elements being locked to provide a specific gear, said control system comprising: a vehicle speed condition monitoring means for monitoring a speed of the vehicle using a speed-related parameter in relation to a vehicle speed of the vehicle;   frictional condition monitoring means for monitoring a frictional condition of said specific friction coupling element using a friction-related parameter in relation to a friction coefficient of said specific friction coupling element;   throttle condition monitoring means for monitoring an operated condition of an engine throttle using a throttle-related parameter in relation to throttle opening of said engine throttle;   a shift characteristic memory means for storing predetermined first and second shift characteristics defined using parameters in relation to vehicle speed and throttle opening; and   shift control means for selecting said specific friction coupling element to lock based on said first shift characteristic when said friction-related parameter demonstrates that said friction coefficient is low and based on said second shift characteristic when said friction-related parameter demonstrates that said friction coefficient is high, and for determining a gear toward which a gear shift must be caused on the basis of said parameters in relation to a vehicle speed, a friction coefficient of said specific friction coupling element and engine throttle opening, respectively, according to a selected shift characteristic, said gear shift to said specific gear being caused at a vehicle speed lower if said gear shift attributes said second shift characteristic than if said first to second gear shift attributes said first shift characteristic.   
     
     
       15. An automatic transmission control system as defined in claim 14, wherein said specific friction coupling element comprises a brake means including a brake drum and a brake band. 
     
     
       16. An automatic transmission control system as defined in claim 15, wherein a gear shift from a first gear to a second gear is caused at a speed lower if said first to second gear shift attributes said second shift characteristic than if said first to second gear shift attributes said first shift characteristic.